Reaching the end of the level with at least four sniper rounds remaining should not be difficult for most players. A player running low can find one cache of sniper ammunition in the brig in which Keyes is being held, and a second cache is just outside the ship's bridge. Playing through the level with the Bandanna skull will completely eliminate the need to conserve ammo, so the player only needs to remember not to swap out their sniper rifle, something that should not be a problem as the sniper is, understandably, a weapon with no peers in the level.